This invention relates to valve assemblies, and more particularly to a valve assembly suited for use, for example, as part of a mud pump used in well drilling operations.
In a typical oil well drilling or well service operation, a positive displacement, reciprocating piston pump is employed to move the drilling mud. Check valve assemblies are connected both to the pump intake and to the pump outlet to ensure that the mud flow is in one direction only as the piston reciprocates.
Valve assemblies for this purpose must function under harsh conditions because the mud contains abrasive particles which wear the valve parts and larger pieces which make a good seal (when the valve assembly is closed) difficult to attain. The valve assembly must function while fluids containing solids and compounds such as acids, pea gravel, sand, liquid carbon dioxide, glass beads, aluminum pellets, mothballs, rock and granulated salt, walnut hulls and cement are flowing through it. The valve assembly must open and close on each reciprocation of the pump piston (up to 1,000 strokes per minute) and therefore it is subjected to constant jarring shocks. Further, it must operate under relatively high pressure conditions, such as up to 20,000 psi.
A typical prior art valve assembly of this nature includes a metal housing, a metal seat formed in the housing, a metal valve which reciprocates to open and close the flow passage, and an elastomeric insert mounted on the valve. The insert, of course, engages the seat to close the passage. The metal parts are accurately machined, and considerable time and expense have been required to manufacture them.
Numerous prior art designs are known. In addition to those shown in FIGS. 1 to 6 herein, John T. Rogers U.S. Pat. No. 4,860,995 shows a design which purports to avoid some of the problems with prior art valves. The Rogers valve includes a metal body part and a plastic insert which forms an upper guide. The plastic insert also includes a flange part which performs the function of the insert of the earlier valves. The metal body part forms a lower guide and supports the plastic insert when the valve is closed.
It is a general object of the present invention to provide an improved valve for use in, for example, a mud or well service pump.